Two-RF-Driver-Based Negative Ion Source for Fusion R&D

Inductively coupled radio-frequency (RF)-based multidriver negative ion sources form the basis of the ion sources for neutral beam injectors considered for present-day fusion devices. Information on the operational behavior of such multidriver RF sources is limited. Thus, an Indian program on the development and operation of such multidriver sources has been initiated to support and enhance the existing information and thus contribute to the successful development of the large-size multidriver ion sources. Experiments initiated under this program have the objective of understanding the physics and technology of plasma production and its control in the presence of the multidriver coupling. An experimental system consisting of a two-driver-based source powered by a single 1-MHz 180-kW RF generator has been configured for the purpose. It is foreseen that, in the proposed configuration of the source, a plasma of density on the order of 10(18) m(-3) in a volume about 0.5-m(3) chamber shall be produced, and under cesiated conditions (Cs vapor injected into the source), a negative hydrogen ion current on the order of 10-12 A can be extracted at 50 kV. Adequate flexibility has been incorporated in the system design to test the source performance in air or under vacuum. The experiment is supported by extensive optical-, thermocouple-, and probe-based diagnostics to provide information related to the essential plasma parameters such as uniformity, temperature, density, and impurity level.